Transistor



May 19, 1959 L. M. MLA@ Em. l 2,887,629

TRANSISTOR lFiled Feb; 1s. 1957.

Y lNvENroRs` q ouls malus NuLANo .JAN AomANus MANmTvELD AGENT United.A States Patent TRANSISTOR Louis Marius Nijland and Jan Adrianus Manintveld,

Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Application February 13, 1957, Serial No. 639,951

Claims priority, application Netherlan February 29, 1956 8 Claims. (Cl. 317-234) The invention relates to a method of producing a semi-r conductive electrode system, more particularly a transistor, in which a semi-conductive body for example of germanium or silicon is provided with at least one rectifying electrode and one ohmic connection, this structure being then etched and housed in an envelope. 'Ihe invention furthermore relates to a semi-conductive electrode system or device, more particularly a transistor housed yin a vacuum-tight envelope.

The invention is found to be of particular use for transistors, for the purpose of increasing the current amplication factor ach, which is defined by the equation:

wherein I,s and Ib denote the collector current and the base current respectively, measured `at a constant collector voltage Vc.

It is already known that the current amplification factor of germanium transistors and more particularly that of silicon transistors can be enhanced by coating the semi-conductive surface with a layer of oxidizing material, for example, of lead minium, zinc chromate or strontium chromate and that organic compounds may be used for this purpose. However, experiments have proved that transistors thus manufactured are often not stable, especially at high temperatures.

The invention has for its object to provide a method of producing a semi-conductive electrode system having a high current amplification factor and great stability. It has furthermore the advantage that the surface of the semi-conductive body can be provided in a simple manner with very thin layers, even layers of molecular thickness, producing these favourable effects.

In accordance with the invention the semi-conductive body with its electrode and ohmic connection is, after the etching operation, introduced into a space containing at least one of the halogens and/or their hydrates with the exception of elemental lluorine. The element fluorine is excepted, since it is unserviceable owing to its great reactivity. In practice it has been found that almost immediately an increase in the current amplication factor is obtained, if the space into which the semi-conductive body is introduced contains even a very small quantity of vapour of one or more of these elements and compounds. The effect aimed at by the invention is therefore also realized if the milieu or atmosphere contains a dissociating substance capable of producing a marked vapour pressure of the halogens and/ or the hydro-halides. It should further be noted, that the results obtainable by the method according to the invention are in general not dependent upon the special etching solution employed.

Particularly suitable are found to be hydrochloric acid and hydro-iluoric acid. The eiect is further increased if the space contains, in addition, water vapour.

A particular embodiment of the invention consists in that the semi-conductive body with its electrode and ohmic connection is accommodated in a vacuum-tight 2,887,629 Patented May 19, `1959 ICC body is made of silicon, since the conventional means,

which yielded satisfactory values of the current amplication factor with germanium, do not give satisfactory results with silicon.

In one embodiment of a semi-conductive electrode,

system, more particularly a transistor according to the invention, the vacuum-tight envelope contains at least one of the halogens and/ or one of their compounds with hydrogen, with the exception of the element tluorine. The envelope may furthermore contain water vapour.

It should be noted, that this gaseous atmosphere atects favourably not only transistors, but will yield similar results with other semi-conductive electrode systems, when the method according to the invention is employed.

One embodiment of a semi-conductive electrode system according to the invention, to which the invention-is however not limited, will now be described withreferencc to the sole figure of the accompanying drawing, which shows, in cross-section, a transistor according to the invention.

Referring now to the ligure, a transistor comprises a thin semi-conductive disc 1, provided with an emitter electrode 2, a collector electrode 3 and an ohmic annular base connection 4. The electrodes 2, 3 and the ohmic connection 4 are each connected to supply conductors 5, 6, 7 passing through a glass pinch 8, and are passed to the outside through the glass base 9, to which a glass bulb 10 is sealed. The envelope (9, 10) contains for instance dry HCl vapour at a pressure of about 104 mm. Hg.

The method according to the invention will now be described more fully with reference to a few examples.

Example 1 An alloy transistor comprising a semi-conductive body consisting of p-type silicon, provided with a base connection, consisting of an alloy of 90% by weight of indium and 10% by weight of copper, and further provided with an emitter electrode and a collector electrode, both consisting of by weight of gold and 25% by weight of antimony, was etched in a bath containing a mixture of a 52% aqueous solution of hydrouoric acid and a 97% aqueous solution of nitric acid in the volume ratio 1:3, and subsequently washed in streaming, distilled deionized Water and dried. After measurement of the current amplilication factor web. Which turned out to be 4.5, the transistor was arranged in a glass envelope containing dry HCl. Owing to this treatment the current amplification factor nach rose almost immediately to 27. During the subsequent pumping off ach increased further and attained a maximum value of 31.5 at a pressure of about 104 mm. Hg, after which the glass envelope was sealed tight. In order to check the stability of the transistor the assembly was then heated, whereby acl, increased continuously and reached a value of 37 at 180 C. Durlng cooling to room temperature the same range was reversed, which confirms the stability of the transistor.

Example 2 A silicon alloy transistor such as described in Example l was introduced after the etching operation into a space,

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containing apart from HF also water vapour, of which the vapour pressure was about one hundredth of that of HF. Before this treatment the current amplification factor atcb was 6; after this treatment it had increased to 25. 'The 'transistor was then housed in a vacuum-tight envelope and heated to 180 C., at which temperature ach was`35. After cooling to room temperature nach was again 25, which conrms the stability of the transistor.

Example 3 -Of an 'alloytransistor such as described in Example l the current amplification factor web was after the etching operation. The transistor was then introduced into a space containing dry HC1; after this treatment ach had increased to l27. By adding water vapour .to an amount of about 1% relative to .the HCl zcbrose'to a value 30.

yExarrwle 4 An alloy transistor comprising a semi-conductive body consisting of n-type germanium, provided with `a. base electrode consisting-of an alloy vof97% by weightoftin an'd'3% by weight of antimonyfand'further `provided with an emitter 'electrode and a'collector electrode, both consisting of indium, was etched ein a bath composed of 2 volume parts 52% aqueous solution of HF, 2 volume parts 97% aqueous solution of HNO3, and 5 volume parts H2O, and subsequently washed in distilled water and dried. The current amplification vfactor amounted to 30 after this etching treatment. The transistor Was then sealed in a glass envelope containing HF yand water vapour. After this treatment ach had increased to 90. yDuring the subsequent heating acbrose to a value 100 at a temperature of 70 C. During the Icooling to room temperature the same range wasreversed, which confirms the stability of the transistor.

Example 5 An alloy transistor such as described in Example l, had a current amplification factor nach of 2.7 after the etching operation. The transistor was then introduced into an envelope containing apart from bromine vapour, water vapour. Thus agb increased to 18.5. During the subsequent heating ach increased further to obtain a value 24at 180 C. After cooling to room temperature cb decreased practically to the initial value viz. y17.5.

What is claimed is:

'1. A semi-conductive device comprising an etched semiconductive body with plural lelectrode connections to said body and possessing a current amplication factor Whose value depends on the 'surrounding atmosphere, a sealed 50 envelope enclosing lthe'body with its connections, and an atmosphere in said envelope comprising water vapor and a substance selected from the group consisting of chlorine, bromine, iodine, and hydrogen compounds of the latter and of iluorine.

2. A semi-conductive device comprising an etched semiconductive body selected Afront the group consisting of germanium and silicon and with ohmic and rectifying electrode connections to said body, a vacuum-tight sealed envelope enclosing the body with its connections, and an atmosphere in said envelope comprising water vapor and a substance selected from the group consisting of chlorine, bromine, iodine and hydrogen compounds of the latter and of iluorine.

3. A device as set forth in claim 2 wherein the atmosphere is at a pressure below 10-2 mm. ofrnercury.

4. A device as set forth in claim 2 wherein the substance is hydrochloric acid.

5. A semi-conductive device comprising an etched semiconductive body selected from the group consisting of germanium and silicon with ohmic and yrectifying electrode connections to said body, a vacuum-tight sealed envelope enclosing the body with `its connections, and an atmosphere in said envelope comprising a substance selected from the group consisting of hydrofluoric acid and hydrochloric acid.

6. A method manufacturing a semi-conductive device comprising a semi-conductive body and plural electrode connections to said body and possessing a current amplication factor whose value depends on the surrounding atmosphere, comprising etching the body, and thereafter introducing the body With its electrode connections into an atmosphere containing Water vapor and a substance selected from the group consisting of chlorine, bromine, iodine, and hydrogen compounds of the latter and of uorine.

7. A method of manufacturing a semi-conductive dcvice comprising a semi-conductive body selective from the group consisting of germanium and silicon and having ohmic and rectifying electrode connections to said body, comprising etching `thebody, and thereafter introducing the body with its electrode connections into an atmosphere containing Water vapor and a substance selected from the group consisting of chlorine, bromine, iodine, and hydrogen lcompounds of the latter and of luorine.

8. A method as set forth in claim 7 wherein the `atmosphere is partly vremoved and then the body with its connections sealed-off in a vacuum-tight envelope.

2,812,480 l'Ellis Nov. 5, 1957 

1. A SEMI-CONDUCTIVE DEVICE COMPRISING AN ETCHED SEMICONDUCTIVE BODY WITH PLURAL ELECRTODE CONNECTIONS TO SAID BODY AND POSSESSING A CURRENT AMPLIFICATION FACTOR WHOSE VALUE DEPENDS ON THE SURROUNDING ATMOSPHERE, A SEALED ENVELOPE ENCLOSING THE BODY WITH ITS CONECTIONS, AND AN ATMOSPHERE IN SAID ENVELOPE COMPRISING WATER VAPOR AND A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF CHLORINE BROMINE, IODINE, AND HYDROGEN COMPOUNDS OF THE LATTER AND OF FLUORINE. 